Frangible, flexible printed circuit sensor fracturable by derailed cable

ABSTRACT

A cable derailment sensing device and method for use with pulley means having a cable carried thereby to detect derailment of the cable from the pulley means is disclosed. The sensing device includes a brittle frangible element positioned by mounting means for impact thereof by the cable upon derailment, and the frangible element carries an electrically conductive path thereon which is connected to electrical sensing circuitry. The brittle sensing element is formed of a material which is vibration and fatigue resistant and has sufficient durability to withstand accidental jarring. The electrically conductive path may be formed by printed circuit techniques on a surface of a frangible element such as a printed circuit board. The brittle frangible element is preferably prestressed by the mounting means to insure complete fracturing thereof upon impact by the cable.

United States Patent [191 Kunczynski July 2, 1974 1 FRANGIBLE, FLEXIBLEPRINTED CIRCUIT SENSOR FRACTURABLE BY DERAILED Primary ExaminerJames R.Scott CABLE I Attorney, Agent, or Firm-Warren, Rubin & [75] Inventor:Jan K. Kunczynski, Tahoe City, Ch'ckermg Calif. [73] Assignee: LiftEngineering & Mfg., Inc., [57] S T Carson City, A cable derailmentsensing device and method for use with pulley means having a cablecarried thereby to [22] Flled: June 1973 detect derailment of the cablefrom the pulley means [21 Appl 375 09 is disclosed. The sensing deviceincludes a brittle frangible element positioned by mounting means forimpact thereof by the cable upon derailment, and the [52] US. Cl.200/6L08 frangible element Carries an electrically conductive [51] Int.Cl. HOlh 35/00 path thereon which is connected to electrical Sensing[58] Fleld of Search ZOO/61.08, 61.13, 61.18, Circuitry. The brim6Sensing element is formed of 8 200/166 PC; 174/110 SR; 317/ I01 F;material which is vibration and fatigue resistant and 339/80;340021419303 has sufficient durability to withstand accidental jarring.The electrically conductive path may be formed [56] References C'ted byprinted circuit techniques on a surface of a frangi- UNITED STATESPATENTS ble element such as a printed circuit board. The brittle3,230,327 H1966 McDowell ZOO/61.08 frangible elrment is PreferablyPrestressed y the 3,651,287 3/1972 Rubenstein 200/166 PC X mountingmeans to insure complete fracturing thereof 3,676,814 7/1972 Trunzo etal 174/110 SR X u on im act b the cable. 3,745,276 7/1973 McPherson200/6108 p p y 3,745,288 7/1973 11 Claims, 3 Drawing Figures Reimer200/166 PC FRANGIBLE, FLEXIBLE PRINTED CIRCUIT SENSOR FRACTURABLE BYDERAILED CABLE BACKGROUND OF THE INVENTION I carrier sheaves isparticularly troublesome and dangerous is in a chairlift of the typeemployed to transport skiers. Most chairlifts involve several thousandfeet of cable stretched over periodically spaced pulleys mounted ontowers. Some chairlifts are in excess of l mile in length, and constantsupervision and observation of the movement of the chair-carrying cableover the pulleys along the entire length of the lift is normally notpossible. Moreover, the method of attaching the chairs to the cableinherently prevents the use of cable derailment prevention structures onone side of the ca ble.

Occasionally, the cable for a chairlift has been known to becomederailed from one or more of the pulleys on which it is mounted. Usuallythe 'cable will be caught by a supporting structure adjacent the pulleysor sheaves upon derailment so that danger to the passengers of thechairlift is minimized. If the chairlift is not stopped almostimmediately after derailment, however, there is some danger that thederailed cable will further be pulled from the supporting structure orentangled in the same. If this should happen, there is a substantialhazard in steep mountainous terrain to personnel riding the chairlift.

In order to increase the safety of the chairlift, attempts have beenmade to sense derailment of the cable so that the lift can beimmediately shut down and the cable replaced on the sheaves. Oneapproach to this problem has been to stretch an electrically conductivewire transversely of and immediately adjacent tothe cable in a locationwhich will cause the wire to be severed in the event that the cable isderailed. This wire is then connected to sensing circuitry which can bemonitored at a central location to automatically shut down operation ofthe lift and indicate where the derailment has taken place.

It has been found, however, that sensing devices as above described havenot been reliable. Upon derailment of the cable, it will impact thewire, but often the wire merely bends and stretches without becomingsevered. In this situation, the sensing circuitry will not detect aderailment, and the lift will continue to operate under the extremelyhazardous derailed condition. Additionally, sometimes the cable willimpact against the sensing wire and sever the same, but trap the piecesof wire between the cable and supporting structure. When this occurs,the electrical circuit can be completed through the cable, even thoughthe sensing wire is severed. Therefore, a condition again exists inwhich the sensing circuitry will not shut down operation of the lift.Obviously, when either one of these defects occurs a complete breakingof the wire and circuits may eventually result, but only after the cablehas continued to be advanced for a period of time in the derailedcondition.

The reliability of the wire--type sensing devices is further reduced bythe adverse environmental conditions in which the sensing device mustoperate. Thus, in the summer the wire is subject to high temperaturesand ultraviolet bombardment at high altitudes, while in the winterextremely cold conditions are encountered. Still further, the build-upof snow on the tower supporting the sheaves may enhance the likelihoodthat the wire will not be cleanly severed and the circuit broken uponderailment of the cable.

Another approach has been to employ proximity switches to sense thechange in or proximity of the cable, for example, when it jumps thesheaves. These switches are often not well suited for the adverseenvironmental conditions, but more importantly, they must be set at arelatively insensitive level to avoid repetitive false alarms. Thus, theproximity switch cannot sense short duration changes in the location ofthe cable and usually has a 3 or 4 second built-in delay. This delay,however, can result in an extremely hazardous condition of advancementof the cable while derailed, particularly when the cable cannot bestopped instantaneously even when the proximity switch finally signalsto stop.

Finally, some attempts have been made to use cast iron rods as thesensing element by positioning the rods for impact by the cable when itjumps the sheaves. The rods act as an electric conductor, but theirbrittle nature prevents stretching upon impact. This approach has beenfound to be unsatisfactory because tower vibration when the cable isrunning has fatigued and fractured the rods. Additionally, the fragilenature of the rods makes them subject to fracture when bumped duringinstallation or when jarred directly or indirectly by passengers on thechairlift.

Accordingly, it is an object of the present invention to provide a cablederailment sensing device and method which provides improved reliabilityand safety in connection with sensing the derailment of a cable frompulley means.

Another object of the present invention is to provide a cable derailmentsensing device which will reproducibly function in adverse environments,is fatigue and vibration resistant and can withstand accidental impactsupon installation and use.

Another object of the present invention is to provide a cable derailmentsensing device which may be readily adapted to a variety ofapplications, is easy and inexpensive to manufacture, is easy toinstall, may be readily replaced, and is particularly well suited foruse with chairlifts, ski lifts, and the like.

The cable derailment sensing device of the present invention has otherobjects and features of advantage some of which will be set forth inmore detail or will be apparent from the description hereinafter and theaccompanying drawing.

SUMMARY OF THE INVENTION The cable derailment sensing device of thepresent invention is formed for use with pulley means having a cablecarried thereby. The device includes sensing means, mounting meanspositioning the sensing means adjacent the pulley means for impact bythe cable upon derailment from the pulley means, and electrical sensingcircuitry connected to the sensing means. The improvement of the presentinvention is comprised, briefly, of the sensing means being formed as abrittle frangible element formed of a fatigue resistant and vibrationwithstanding material having an electrically conductive path ofinsubstantial strength carried thereby and electrically connected to thesensing circuitry. The brittle frangible element, preferably afiberglass printed circuit board, has a strength and brittleness causingcomplete fracturing of the element at at least one position along theelectrically conductive path upon impact of the element by the cable andyet will not fatigue or be severed by vibration or normal operationaljarring. The electrically conductive path is preferably printed on asurface of the brittle frangible element by printed circuit techniques,and the brittle frangible element is mounted in a prestressed condition,preferably by twisting, to insure complete fracturing of theelectrically conductive path upon impact by the cable.

The method of sensing the derailment of a cable from pulley means of thepresent invention is comprised of mounting a brittle, frangible andfatigue resistant element, such as a printed circuit board, having anelectrically conductive path imprinted thereon adjacent the pulley forimpact by the cable, and electrically connecting the path to sensingcircuitry.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top, fragmentary,cross-sectional view of a sensing device constructed in accordance withthe present invention and mounted adjacent a set of pulleys.

FIG. 2 is a fragmentary, side elevational view, in cross-section of thesensing device of FIG. 1.

FIG. 3 is a top plan view of a brittle frangible element shown installedin FIGS. 1 and 2 and suitable for use in the sensing device of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2,pulley means or assembly, generally designated 21, is shown with cableor flexible tendon 22 carried thereby. Pulley assembly 21 includes adouble-ended yoke 23 to which groove pulley wheels or sheaves 24 aremounted. Sheaves 24 are pivoted by pins 26 for rotation with respect toarms 27. Mounted on the ends of arms 27 (not shown in the drawing) is asecond sheave or pulley wheel, and arms 27 are preferably pivotallymounted to yoke 23 by a connection also not shown.

Extending through the end wall 28 of tower arm structure 29 is rodmember 31. The double-ended yoke 23 is secured on rod member 31 by block32 (FIG. 2) which may be selectively inserted in groove 33 at the end 34of the cylindrical rod and held in place by bolt 35. In order to providefor angular adjustment of the yoke with respect to tower arm structure29, mutually perpendicular and threaded bolts 36 and 37 are provided andextend through mutually perpendicular openings in end 38 of rod 31. Asbest may be seen in FIG. 2, pulley wheels or sheaves 24, when employedin a Chairlift, preferably are formed with a grooved resilient insert39, such as a rubber material, on which cable 22 rides and with sideflanges 41, which are inwardly tapered to resist derailment of thecable.

As thus far described, the pulley assembly and tower structure areformed in a conventional manner, and

further details thereof have been omitted for the sake of simplicity. Inthe conventional chairlift, the chairs are attached to cable 22 by cablegrips, annd the chairs are located periodically over the length of thecable. The chairs and passengers carried thereby exert a considerabledownward force on cable 22 as it passes over the sheaves. Additionally,however, considerable lateral forces are exerted on cable 22 by reasonof wind loading on the chairs, lateral rocking of the chairs,misalignment of the sheaves from tower to tower. etc., which lateralforces tend to contribute toward and result in occasional derailments.

In order to be able to sense derailment of the cable from the sheaves sothat the derailment can be located and the cable motion stopped, sensingmeans, generally designated 42, is mounted in mounting means, generallydesignated 43, adjacent pulley means 21 for impact by the cable uponderailment. As shown in FIGS. 1 and 2, sensing means 42 is mountedbeneath cable 22 and extends outwardly of both sides of the sheaves.Thus, when cable 22 jumps flanges 41 of the pulleys, the substantialdownward force of the weight on the cable will cause the cable to dropdownwardly immediately as it passes over the flanges to impact thesensing means adjacent the side walls of the pulleys. It should benoted,

however, that there are tower installations in which the pulleys arelocated in a relatively low position with respect to the cable and ineffect hold the cable down against a very substantial upward force. Inthis situation, the cable would be located on the underside of pulleymeans 21 as viewed in FIG. 2 with sensing means 42 positioned under yokecarrying arm 31 so as to be impacted by the cable as it snaps upwardlyupon derailment.

The improvement of the present invention is comprised of sensing means42 being formed as a brittle, frangible and fatigue resistant element 44having an electrically conductive path 46 (best seen in FIG. 3) carriedthereby and electrically connected at points 47 and 48 by conductors 49and 51 to electrical sensing circuitry, generally designated 52. Brittlefrangible element 44 has a brittleness selected to cause completefracturing thereof at at least one position along electricallyconductive path 46 and yet is formed of a material which will notfatigue, is impervious to vibration and can withstand accidental jarringor impact. In most chairleft installations cable 22, if derailed fromsheaves 24, will apply a minimum downward static force of about 750 to1,000 pounds. The impulse loading of this downward force on frangibleelement 44 will, therefore, be relatively high. If frangible element 44is formed from a board-like strip of material, such as a thermosettingresin or thermosetting plastic having a brittleness which will insurecomplete fracture of the strip under a load of about 200 to 300 pounds,the sensing strip will be broken in many places along conductor path 46upon impact by the cable. Many thermosetting resins and plastics have ahigh resistance to fatiguing and are largely uneffected by vibration.Thus, they are particularly well suited for use in the apparatus andmethod of the present invention.

It is a feature of the present invention that sensing element or strip44 have electrically conductive path 46 imprinted thereon using printedcircuit techniques so that the conductive path has relativelyinsubstantial physical strength and will not interfere with or resistcomplete fracturing of the sensing element. Printed circuit techniquesare particularly well suited for this purpose since they provide thenecessary electrically conductive path without adding to the strength ofthe frangible element. Moreover, stretching of the electricallyconductive path, as has been common with wire-type sensors, will notoccur.

As best may be seen in FIG. 3, it is preferable that the electricallyconductive path be printed as an openended loop connected at open ends47 and 48 adjacent first end 53 to sensing circuitry 52. The use of theloop is advantageous since it provides a convenient structure forelectrical connection to sensing circuitry 52, and severing eitherbranch of the loop will cause an open circuit which can be sensed bycircuitry 52. Additionally, the loop at second end 54 passes around aportion of the sensing strip mounting means, as will be set forth indetail hereinafter, which further increases the likelihood of severingconductive path 46. lmpact of cable 22 on the sensing strip may pullsecond end 54 thereof away from mounting means 43, causing the mountingmeans to sever path 46.

In order to further insure that brittle frangible sensing strip 44 andelectrically conductive path 46 are fractured by impact of the cable, itis another important feature of the present invention that the sensingstrip is mounted in a prestressed condition. When brittle frangibleelement 44 is formed as a board-like strip prestressing by mountingmeans 43 can be accomplished by forming the mounting means to mountstrip 44 in a longitudinally twisted orientation between first end 53and second end 54. This prestressing condition does not introduce astress which resists fracturing, but instead encourages fracturing.Thus, at first end 53 a pair of openings 56 and 57 may be formed in thefrangible sensing strip, and mounting means 43 at end 53 may becomprised of a pair of fasteners 58 passing through clamp 59, andopenings 56 and 57 and into block 61 to secure end 53 of the fasteningstrip in generally horizontal orientation. Clamp 59 further secures aprotective sleeve 62 to the sheave supporting yoke 23. Sleeve 62 coversconductors 49 and 51 and passes through grommet 63 into the interior oftower arm structure 29. While the conductors 49 and 51 are shown to passout to the sensing circuitry through the side wall of the arm structure,this is merely a schematic representation since the conductors wouldnormally extend transversely the length of the arm and pass out of thetower to the sensing circuitry through a grommet similar to grommet 63.

As shown in FIGS. 1 and 2, it is preferable that strip 44 be twistedbetween ends 53 and 54 by about 90. Thus. mounting means 43 is furthercomprised of an upstanding arm 66 formed with a vertically oriented slotor groove 67 dimensioned for receipt of second end 54 of the sensingstrip. Slot 67 opens to the top 68 of arm 66 so that strip 44 may beinserted in the slot from the top thereof. This is particularlyconvenient when the sensing strips must be replaced. in order to holdthe sensing strip in arm 66, a pin 69 is positioned through opening 71in second end 54 of the frangible strip. Pin 69 engages the outwardlysloped underneath surface of arm 66 beyond the slot and prevent upwarddisplacement of the strip out of slot 67. Pin 69, moreover, is in aposition with respect to conductive path 46 to break the conductive pathin the event that cable 22 pulls the sensing strip inwardly from arm 66.

Since the grips which secure the chairs to the cable must pass over andbeyond the sheaves, it is not possible to provide a structure which willprevent derailment of the cable outwardly of the tower. Thus, there is agreater likelihood of cable derailment over the side of the sheaves awayfrom the tower than derailment of the cable toward the tower. Thus, itis a further feature of the present invention that strip 44 ispositioned in mounting means 43 with the portion of the strip mostlikely to be impacted upon derailment of the cable oriented with one ofside edges 72 or 73 positioned to be impacted first by the cable. Edge72, therefore, is oriented upwardly on the side of sheaves 24 away fromtower arm structure 29 since this is the area in which derailment ismost likely to occur. Orientation of strip 42 in an edgewise manner inthis area further enhances the likelihood of complete severing of theconductive path carried thereby by concentrating the impact of the cableon a small area of the brittle strip and maximizing the elongation ofthe lower edge 73 of the strip for any downward deflection upon a cableimpact. Since the strip is a brittle material, any substantialelongation of edge 73 will start fracturing. The likelihood offracturing beginning at the edge of the strip 44 makes it furtheradvantageous and a feature of the present invention to positionconductive path 46 to extend along the opposite edges 72 and 73 tomaximize the chance of severing upon cable impact.

The combination of providing a brittle, frangible and fatigue resistantsensing strip having an electrically conductive, looped path ofinsubstantial strength mounted in mounting means in a prestressedcondition, which includes edgewise orientation of the strip, affords ahighly reliable sensing means and safety device. The sensing strip willbe impervious to normal tower vibration and yet will virtually shatterand fly apart upon impact by the cable. Thus, stretching of theconductive path or trapping the path between the cable and thesupporting structure of the sheaves is not possible when the stripfragments upon impact, and false alarms from vibration, fatigue andjarring will not occur.

The brittle frangible element 44 of the present invention may beconveniently formed of a number of different materials. An epoxy glass,without fiber reinforcing, commonly employed in circuit boards andhaving a thickness of about 0.100 inches has been found to beadvantageous. Path 46 may be formed of copper and coated with a solderto afford protection against the adverse weather conditions in which thesensing strip must operate. The length of the strip will vary dependingupon the expected paths through which cable 22 might travel uponderailment. The length and brittleness of the material employed willdetermine the degree of twist which will provide prestressing of thestrip. Numerous fonns of electrical sensing circuitry can be employed inconnection with the sensing device of the present invention. It is onlynecessary that the circuitry be able to differentiate between a closedlooped circuit when the strip is intact and an open circuit uponfracturing of the same. Normally the circuitry would include visual oraudio alarms and would be connected to shut down the power driving thecable. These types of circuits are well known in connection with theoperation of ski lifts and other apparatus.

1 claim:

1. In a cable derailment sensing device for use with pulley means havinga cable carried thereby and including sensing means, mounting meanspositioning said sensing means adjacent said pulley means and for impactby said cable upon derailment from said pulley means, and electricalsensing circuitry connected to said sensing means, the improvementcomprising:

said sensing means being formed as a brittle, frangible and fatigueresistant element formed from an electrically insulating material andhaving an electrically conductive path carried thereby, saidelectrically conductive path being formed as an open ended loop ofelectrically conductive material printed on said sensing means andelectrically connected at the open end thereof to said sensingcircuitry, said element having a brittleness causing complete fracturingthereof at at least one position along said electrically conductive pathupon impact of said element by said cable upon derailment from saidpulley means, and said mounting means supporting said sensing meansadjacent a first and a second end of said sensing means.

2. In a cable derailment sensing device as defined in claim 1 wherein,

said loop commences and terminates and is electrically connected to saidsensing circuitry adjacent said first end of said strip, and said loopis formed to pass around a portion of said mounting means adjacent saidsecond end of said strip.

3. In a cable derailment sensing device as defined in claim 1 wherein,

said mounting means is formed to position said element for impact bysaid cable with said element in a prestressed condition. 4. In a cablederailment sensing device as defined in claim 3 wherein,

said element is formed as a board-like strip, and said strip is securedin said mounting means adjacent the ends of said strip, and saidmounting means is formed to mount said strip in a longitudinally twistedorientation between said ends. 5. In a cable derailment sensing deviceas defined in claim 4 wherein,

said strip is fonned from a resin-based material and is secured in saidmounting means in a substantially horizontal plane adjacent a first endthereof, and said strip is secured in said mounting means in asubstantially vertical plane adjacent a second end thereof to providesubstantially a 90 twist intermediate said ends to prestress said strip.6. In a cable derailment sensing device as defined in claim 5 wherein,

said strip is formed with an opening adjacent said second enddimensioned for receipt of a pin forming a portion of said mountingmeans,

said electrically conductive path is formed as an electricallyconductive material printed on a surface of said strip in an open endedloop extending from said first end of said strip along an edge of saidstrip and around said opening and along an opposite edge of said stripback to said first end;

said mounting means is formed with aslotted portion dimensioned forreceipt of said strip and formed for demountable securement of saidstrip in said slotted portion by positioning of a removable pin throughsaid opening and into engagement with said mounting means adjacent saidslotted portion.

7. [n a cable derailment sensing device as defined in claim 6 wherein,

said strip is positioned in said mounting means with the portion thereofmost likely to be impacted upon derailment of said cable oriented withan edge thereof positioned to be impacted first by said cable. 8. Amethod of sensing the derailment of a cable from pulley means carryingsaid cable comprising:

mounting in a prestressed manner a brittle, frangible, and fatigueresistant printed circuit board having an electrically conductive pathimprinted thereon adjacent said pulley means for impact thereof by saidcable upon derailment from said pulley means;

electrically connecting said electrically conductive path to externalelectrically sensing circuitry formed to sense cable derailment uponbreaking of said electrically conductive path by said cable; an

fracturing of said printed circuit board and said electricallyconductive path by impacting said printed circuit board with said cableupon derailment of said cable from said pulley means.

9. In a cable derailment sensing device for use with pulley means havinga cable carried thereby and including sensing means, mounting meanspositioning said sensing means adjacent said pulley means and for impactby said cable upon derailment from said pulley means, and electricalsensing circuitry connected to said sensing means, the improvementcomprising:

said sensing means being formed as a brittle, frangible and fatigueresistant element formed from an electrically insulating material andhaving an electrically conductive path of insubstantial strengthimprinted thereon, said path being electrically connected to saidsensing circuitry, said element having a brittleness and being mountedin said mounting means to cause complete fracturing thereof atsubstantially any position along said electrically conductive pathimpacted by said cable.

10. In a cable derailment sensing device as defined in claim 9 wherein,

said mounting means is formed to position said element for impact bysaid cable with said element in a prestressed condition.

11. In a cable derailment sensing device for use with pulley meanshaving a cable carried thereby and including sensing means, mountingmeans positioning said sensing means adjacent said pulley means and forimpact by said cable upon derailment from said pulley means, andelectrical sensing circuitry connected to said sensing means, theimprovement comprising:

said sensing means being formed as a brittle, frangible and fatigueresistant printed circuit board formed of an electrically insulatingmaterial and having an electrically conductive path of insubstantialstrength imprinted thereon, said path being electrically connected tosaid sensing circuitry.

1. In a cable derailment sensing device for use with pulley means havinga cable carried thereby and including sensing means, mounting meanspositioning said sensing means adjacent said pulley means and for impactby said cable upon derailment from said pulley means, and electricalsensing circuitry connected to said sensing means, the improvementcomprising: said sensing means being formed as a brittle, frangible andfatigue resistant element formed from an electrically insulatingmaterial and having an electrically conductive path carried thereby,said electrically conductive path being formed as an open ended loop ofelectrically conductive material printed on said sensing means andelectrically connected at the open end thereof to said sensingcircuitry, said element having a brittleness causing complete fracturingthereof at at least one position along said electrically conductive pathupon impact of said element by said cable upon derailment from saidpulley means, and said mounting means supporting said sensing meansadjacent a first and a second end of said sensing means.
 2. In a cablederailment sensing device as defined in claim 1 wherein, said loopcommences and terminates and is electrically connected to said sensingcircuitry adjacent said first end of said strip, and said loop is formedto pass around a portion of said mounting means adjacent said second endof said strip.
 3. In a cable derailment sensing device as defined inclaim 1 wherein, said mounting means is formed to position said elementfor impact by said cable with said element in a prestressed condition.4. In a cable derailment sensing device as defined in claim 3 wherein,said element is formed as a board-like strip, and said strip is securedin said mounting means adjacent the ends of said strip, and saidmounting means is formed to mount said strip in a longitudinally twistedorientation between said ends.
 5. In a cable derailment sensing deviceas defined in claim 4 wherein, said strip is formed from a resin-basedmaterial and is secured in said mountIng means in a substantiallyhorizontal plane adjacent a first end thereof, and said strip is securedin said mounting means in a substantially vertical plane adjacent asecond end thereof to provide substantially a 90* twist intermediatesaid ends to prestress said strip.
 6. In a cable derailment sensingdevice as defined in claim 5 wherein, said strip is formed with anopening adjacent said second end dimensioned for receipt of a pinforming a portion of said mounting means, said electrically conductivepath is formed as an electrically conductive material printed on asurface of said strip in an open ended loop extending from said firstend of said strip along an edge of said strip and around said openingand along an opposite edge of said strip back to said first end; saidmounting means is formed with a slotted portion dimensioned for receiptof said strip and formed for demountable securement of said strip insaid slotted portion by positioning of a removable pin through saidopening and into engagement with said mounting means adjacent saidslotted portion.
 7. In a cable derailment sensing device as defined inclaim 6 wherein, said strip is positioned in said mounting means withthe portion thereof most likely to be impacted upon derailment of saidcable oriented with an edge thereof positioned to be impacted first bysaid cable.
 8. A method of sensing the derailment of a cable from pulleymeans carrying said cable comprising: mounting in a prestressed manner abrittle, frangible, and fatigue resistant printed circuit board havingan electrically conductive path imprinted thereon adjacent said pulleymeans for impact thereof by said cable upon derailment from said pulleymeans; electrically connecting said electrically conductive path toexternal electrically sensing circuitry formed to sense cable derailmentupon breaking of said electrically conductive path by said cable; anfracturing of said printed circuit board and said electricallyconductive path by impacting said printed circuit board with said cableupon derailment of said cable from said pulley means.
 9. In a cablederailment sensing device for use with pulley means having a cablecarried thereby and including sensing means, mounting means positioningsaid sensing means adjacent said pulley means and for impact by saidcable upon derailment from said pulley means, and electrical sensingcircuitry connected to said sensing means, the improvement comprising:said sensing means being formed as a brittle, frangible and fatigueresistant element formed from an electrically insulating material andhaving an electrically conductive path of insubstantial strengthimprinted thereon, said path being electrically connected to saidsensing circuitry, said element having a brittleness and being mountedin said mounting means to cause complete fracturing thereof atsubstantially any position along said electrically conductive pathimpacted by said cable.
 10. In a cable derailment sensing device asdefined in claim 9 wherein, said mounting means is formed to positionsaid element for impact by said cable with said element in a prestressedcondition.
 11. In a cable derailment sensing device for use with pulleymeans having a cable carried thereby and including sensing means,mounting means positioning said sensing means adjacent said pulley meansand for impact by said cable upon derailment from said pulley means, andelectrical sensing circuitry connected to said sensing means, theimprovement comprising: said sensing means being formed as a brittle,frangible and fatigue resistant printed circuit board formed of anelectrically insulating material and having an electrically conductivepath of insubstantial strength imprinted thereon, said path beingelectrically connected to said sensing circuitry.